It is already known, in connection with filament yarns, i.e. yarns which are spun from synthetic resin filaments and can be single-thread and/or multiple filament yarns, to produce a thick/thin effect or a thin/thick effect in the yarn by selectively stretching of certain regions to thin the yarn while allowing intervening portions of the yarn to be stretched to a lesser extent or not stretched at all and thereby form thicker regions.
In practice, however, such yarns have not been highly successful since, especially because of the poor crystalline characteristics of the lesser stretched regions, the strength of the yarn can deteriorate rapidly or is limited, especially under the influence of light. The products which are produced have the drawback that the strength of the yarn is limited and, especially with time and exposure to light, tends to reduce drastically. Threads or yarns can then fail, especially with intensive multi-year exposure to intensive light because their strength over time can drop to a third of the starting strength while the elongation to break can fall from say 30% to about 5%, representing a significant qualitative decline.